Morphology-controlled LiNi_1/3Co_1/3Mn_1/3O₂ Cathode Materials For Lithium Batteries And Their Electrochemical Performance

The cathode material is one of the the key components for lithium ion secondary battery, whose morphology makes a significant impact on the electrochemical performance of lithium ion battery. In this paper, controlled preparation of LiNi1/3Co1/3Mn1/3O2 materials with different morphologies and their electrochemical performance have been investigated. The main points are summarized as follows:1. The stepwise co-precipitation method has been successfully used to prepare precursor, in which the COC2O4·2H2O microrod crystallites formed in the first step can effectively template the subsequent formation of MC2O4·xH2O (M= Ni, Co, Mn) microrod. Through post-heat treatment of microrod precursor, LiNi1/3Co1/3Mn1/3O2 one dimensional (ID) hierarchical microrods assembled with nanoparticles have been prepared. Compared with the LiNi1/3Co1/3Mn1/3O2 microsized particles as cathode material for lithium ion batteries, the LiNi1/3Co1/3Mn1/3O2 1D hierarchical microrods with pores and voids exhibit better reversible capacity, initial coulombic efficiency, rate capability and cycling stability. They deliver initial specific discharge capacity of 163.3 mAh g-1 at rate of 0.1 C with an initial coulombic efficiency of 92%. At 20 C, the specific discharge capacity still remain 104.9 mAh g-1. After 160 cycles, they achieve a discharge capacity of 136.2 mAh g-1 at 0.5 C with a capacity retention of 89.5%. Even at 10 C, the capacity retention reach 85.3% after 100 cycles. The excellent electrochemical performance can be attributed to the novel hierarchical microrod structure, in which the first nanoparticles shorten the diffusion path of electron and lithium ion and benefit for their transfer, and the second microrods provide good accommodation for the strain relaxation during charge and discharge.2. LiNi1/3Co1/3Mn1/3O2 cathode materials were successfully synthesized by using surfactant-assisted co-precipitation method, and the impact of different surfactants on its morphology was explored. The results show that the product by nonionic surfactant (PEG 400) has irregular particle morphology; while the product shows jujube stone-like morphology with participation of anionic surfactant (SDBS); and the product by cationic surfactant (CTAB) exists in spherical, diamond-shaped or rod morphology. The electrochemical properties of the samples were characterized and the results show that the product with jujube stone-like morphology which was synthesized by anionic surfactant SDBS exhibits the greatest initial discharge capacity and better rate capability and cycle performance. The first discharge capacity is 155.9 mAh g-1 with the corresponding coulombic efficiency of 90.1% at 0.1 C and the discharge capacities are 125.3 and 107.6 mAh g-1 at rates of 10 and 20 C, respectively. They deliver a discharge capacity of 150.0 mAh g-1 in the first cycle and 133.2 mAh g-1 after 100 cycles at 0.5 C, and the corresponding capacity retention is 88.8%.